On Sat, Oct 04, 2008 at 02:29:08PM +0100, Dieter wrote:
> > > Surely a "good" USB to RS-232 bridge (if one exists?) or a RS-232
> > > filter/isolator (assuming they exist?) would be *far* less expensive
> > > than the server class alpha you suggest below.
> >
> > It depend on how much RS232 you need and how many slots the OP has free.
> > Nevertheless a "good" RS232 bridge if needed in number are not cheap
> > either - ntoe that you can get affordable PCI extenders as well.
>
> The PCI expanders I've seen cost almost as much as getting an entire
> additional machine.
For PCI you are right, but Exsys for example makes extenders with PCIe
uplinks for a good price.
> > Well the AS4100 I have already has 8 slots which is not that uncommon
> > for alpha servers.
>
> I'd call an alpha with only 8 slots a workstation class machine. It
> wouldn't take much to fill up 8 slots.
It is not the biggest server class, but I wouldn't put it on my desk
either.
> > > USB to RS-232 bridge could be a good solution, if I knew which
> > > make&model of bridge worked well with *BSD. Poking around on the web
> > > I can't even find what chip they have inside.
> >
> > Really forget about USB to RS232.
> > It is not the chip which is the problem it is the principal.
> > You really need galvanic isolation, because USB can't handle ground
> > loops, which no cheap device has.
> > You can use any kind of chip with propper isolation, but then it
> > is likely more expensive than any other kind of solution.
>
> I assume this is marketing driven. Adding a few optos can't
> increase the manufacturing cost *that* much. Sounds like a
> market opportunity for someone.
You also need a DC-DC converter to get power behind the isolation and
8 opto channels.
It wouldn't increase manufactoring costs that much if produced in
numbers, but it would make these devices about two or three times
bigger.
Another point is the additional power requirement.
There are alternatives for optos, that don't consume that much power,
but they are more expensive and you still have the loss for the DC-DC.
Power consumption is an important factor for mobile computing.
So yes - this is marketing driven, but not only for prices.
I produce 12V adapters myself, so I know the size requirements
for adding DCDC converters.
Guess I will add optos one day.
But even those without are already too expensive for adding terminals
compared to e.g. ethernet based RS232.
--
B.Walter <bernd_(_at_)_bwct_(_dot_)_de> http://www.bwct.de
Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.
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